Polyphenylene ether resins have been modified with polyamide resins to provide a wide variety of beneficial properties such as excellent heat resistance, chemical resistance, impact strength, hydrolytic stability and dimensional stability. The improved properties of polyphenylene ether-polyamide compositions have found great utility in thermoplastic applications which take advantage of such properties. Exterior automotive applications such as body panels and wheel covers all benefit from the improved thermal properties of polyphenylene ether-polyamide compositions (PPE/PA compositions). In typical automotive applications such as a fender part, a satisfactory thermoplastic must be capable of providing satisfactory properties over a wide range of end-use temperatures.
Although many important thermoplastic applications for PPE/PA compositions require that the resin be impact modified to provide adequate performance, the ductile behavior of such reasons is often overlooked.
Ductile behavior is an important physical property for thermoplastics in many applications, but particularly for automotive parts which may experience extremely rigorous conditions at very low temperatures. The mode of failure for a part, whether ductile or brittle failure, at a given temperature is also an important indication of the utility of the thermoplastic. Improvements in low temperature ductile-brittle transitions will increase the opportunity for polyphenylene ether-polyamide compositions to adequately service thermoplastic applications where such properties are required or desired. Many conventional, rubber-like impact modifiers offer advantages and disadvantages but do not provide the range of ductile behavior improvement offered by the present invention. Conventional impact modifiers for polyphenylene ether-polyamide compositions can be costly and ineffective compared to the impact modification system described herein.
It has now been discovered that polyphenylene ether-polyamide compositions can be improved by combining the base resin with a modifier comprised of a partially hydrogenated diblock copolymer of styrene and ethylene-propylene in accordance with the description below. Such compositions exhibit the superior properties normally associated with compatible polyphenylene ether/polyamide compositions as well as unexpectedly improved ductile behavior.